Are Americans losing their faith?

What’s one of the fastest-growing segments of U.S. society? According to a Pew Research Center poll released Tuesday, it could be the religiously unaffiliated.

Over a five-year period, the number of Americans who described themselves as not identifying with any religion rose by a third to 19.6 percent of the U.S. public — nearly one in five Americans this year.

That change is even more pronounced among those under the age of 30, which reached an all-time high for Pew polling at one-third of respondents. By contrast, only about 10 percent of those 65 and older say they are religiously unaffiliated.

And while nearly three out of four Americans still identify themselves as Christians — 73 percent this year, down 5 points from 78 percent in 2007 — fewer than half identify themselves as Protestants, with that number now at 48 percent, 5 points down from ’07. Catholics were fairly steady going from 23 percent of the population to 22 percent over the five-year period, while Mormons (2 percent) and Orthodox (1 percent) were unchanged. Other faiths were a combined 6 percent, though that is a 50 percent increase from the 4 percent in that category in ’07.

In fact, the long-term trends, according to the polls, show that most of the decline is coming from white Protestant ranks. Catholics were at 26 percent of the population in 1972 and were at 25 percent in 2010. Protestants fell from 62 percent in ’72 to 51 percent on ’10, while those with no affiliation rose from 7 percent to 18 percent over that 38-year period.

Meanwhile, 3.3 percent this year described themselves as agnostic, up from 2.1 percent five years ago, and 2.4 percent said they were atheists, up from 1.6 percent.

About 13.9 percent of Americans this year said they had no particular religion, up from 11.6 percent in ’07. That doesn’t mean they have no faith — two-thirds of the group believe in God, though less than half are certain of it — and a third say religion is at least somewhat important to them, with 5 percent of the group saying they attend religious services weekly. About 42 percent of the unaffiliated say they are neither religious nor spiritual, but 55 percent describe themselves as either religious (18 percent) or spiritual but not religious (37 percent), while more than one in five (21 percent) prays every day.

Meanwhile, a declining share of the U.S. population says it never doubts the existence of God, dropping to 80 percent this year from 88 percent in 1987. Two-thirds of Americans see religion losing influence on society, with 49 percent viewing that as a bad thing for the nation.

Is America losing its faith? A simple question, but the answer isn’t. And in the end, only time will tell.